/*
- * Copyright (c) 2005-2007 Apple Inc. All rights reserved.
+ * Copyright (c) 2005-2012 Apple Computer, Inc. All rights reserved.
*
- * @APPLE_LICENSE_HEADER_START@
- *
- * The contents of this file constitute Original Code as defined in and
- * are subject to the Apple Public Source License Version 1.1 (the
- * "License"). You may not use this file except in compliance with the
- * License. Please obtain a copy of the License at
- * http://www.apple.com/publicsource and read it before using this file.
- *
- * This Original Code and all software distributed under the License are
- * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
+ *
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. The rights granted to you under the License
+ * may not be used to create, or enable the creation or redistribution of,
+ * unlawful or unlicensed copies of an Apple operating system, or to
+ * circumvent, violate, or enable the circumvention or violation of, any
+ * terms of an Apple operating system software license agreement.
+ *
+ * Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this file.
+ *
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
- * License for the specific language governing rights and limitations
- * under the License.
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ *
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
*
- * @APPLE_LICENSE_HEADER_END@
+ * This file implements strlen( ) for the x86_64 architecture.
*/
-/*
- * Strlen, for processors with SSE3.
- *
- * Note that all memory references must be aligned, in order to avoid spurious
- * page faults. Thus we have to load the aligned 16-byte chunk containing the
- * first byte of the operand, then mask out false 0s that may occur before the
- * first byte.
- *
- * We favor the fall-through (ie, short operand) path.
- */
+.globl _strlen
- .text
- .globl _strlen
- .align 4, 0x90
-_strlen: // size_t strlen(char *b);
- pxor %xmm0,%xmm0 // zero %xmm0
- movl %edi,%ecx // copy low half of ptr
- movq %rdi,%rdx // make another full copy
- andq $(-16),%rdi // 16-byte align ptr
- orl $(-1),%eax
- pcmpeqb (%rdi),%xmm0 // check whole qw for 0s
- andl $15,%ecx // get #bytes in aligned dq before operand
- shl %cl,%eax // create mask for the bytes of aligned dq in operand
- pmovmskb %xmm0,%ecx // collect mask of 0-bytes
- andl %eax,%ecx // mask out any 0s that occur before 1st byte
- jz LEnterLoop // no 0-bytes (ie, 1-bits), so enter by-16 loop
-
-// We've found a 0-byte.
-// %rdi = aligned address of 16-byte block containing the terminating 0-byte
-// %ecx = compare bit vector
+/*****************************************************************************
+ * Macros *
+ *****************************************************************************/
-LFoundIt:
- bsf %ecx,%eax // find first 1-bit (ie, first 0-byte)
- subq %rdx,%rdi // get length to start of 16-byte block while we wait
- addq %rdi,%rax // add bytes in 16-byte block
+.macro EstablishFrame
+ push %rbp
+ mov %rsp, %rbp
+.endm
+
+.macro ClearFrameAndReturn
+ pop %rbp
ret
-
-// Loop over aligned 16-byte blocks:
-// %rdi = address of previous block
+.endm
+
+/*****************************************************************************
+ * Entrypoint *
+ *****************************************************************************/
+
+.text
+.align 5
+_strlen:
+// size_t strlen(const char *s);
+//
+// returns the length of the string s (i.e. the distance in bytes from
+// s to the first NUL byte following s). We look for NUL bytes using
+// pcmpeqb on 16-byte aligned blocks. Although this may read past the
+// end of the string, because all access is aligned, it will never
+// read past the end of the string across a page boundary, or even
+// accross a cacheline.
+ EstablishFrame
+ mov %rdi, %rcx
+ mov %rdi, %rdx
+
+// Load the 16-byte block containing the first byte of the string, and
+// compare each byte to zero. If any NUL bytes are present in this
+// block, the corresponding *bit* in esi will be set to 1.
+ and $-16, %rdi
+ pxor %xmm0, %xmm0
+ pcmpeqb (%rdi), %xmm0
+ pmovmskb %xmm0, %esi
+
+// The 16 bytes that we checked for NUL included some bytes preceeding
+// the start of the string, if s is not 16-byte aligned. We create a
+// mask based on the alignment of s which covers only those bits
+// corresponding to bytes that do not preceed s, and check for NULs
+// only in those bits. If we do not find one, we jump to our main
+// search loop.
+ and $0xf, %rcx
+ or $-1, %rax
+ shl %cl, %rax
+ and %eax, %esi
+ jz L_loop
-LEnterLoop:
- pxor %xmm0,%xmm0 // get some 0-bytes
- addq $16,%rdi // advance ptr
-LLoop:
- movdqa (%rdi),%xmm1 // get next chunk
- addq $16,%rdi
- pcmpeqb %xmm0,%xmm1 // check for 0s
- pmovmskb %xmm1,%ecx // collect mask of 0-bytes
- test %ecx,%ecx // any 0-bytes?
- jz LLoop // no 0-bytes, so get next dq
+L_foundNUL:
+// The last 16-byte block that we searched contained at least one NUL.
+// We use bsf to identify the first NUL, and compute the distance from
+// that byte to the start of the string.
+ bsf %esi, %eax
+ sub %rdx, %rdi
+ add %rdi, %rax
+ ClearFrameAndReturn
- subq $16,%rdi // back up ptr
- jmp LFoundIt
+.align 4
+L_loop:
+// Main search loop: check for NUL in a 16-byte block, continuing
+// loop until one is found.
+ add $16, %rdi
+ pxor %xmm0, %xmm0
+ pcmpeqb (%rdi), %xmm0
+ pmovmskb %xmm0, %esi
+ test %esi, %esi
+ jz L_loop
+ jmp L_foundNUL
projects / apple / libc.git / blobdiff